X-ray based instruments are used in a wide variety of industries for many purposes. In those applications that require that the energy of the x-rays be accurately measured it is necessary to calibrate the energy response of the detector system. In some applications the calibration must be carried out at frequent intervals. The term ‘x-ray’ as used herein and in any appended claims applies to all photons in the range from about 0.5 keV to 100 keV and greater energies as well, encompassing all radiation capable of penetrating solid matter, whether originating from atomic or nuclear transitions in radioisotopes, x-ray tubes, plasma emitters, or any other source. Such radiation may also be referred to as ‘penetrating radiation’.
The calibration of energy-dispersive instruments has traditionally used either a radioactive source or an x-ray tube. For example, the radioactive source may direct monoenergetic photons of precisely known energy into the detector, or, alternatively, a radioactive source or x-ray tube may induce fluorescence in a known target material and the monochromatic x-rays from the target may be directed into the detector. These traditional methods typically require that a calibration target be moved in and out of the x-ray beam path, or that a ponderous shield be positioned to intervene between the source and the calibration target. Radioactive calibration sources, which cannot be turned off, may require licensing and diligent safety procedures. It is thus desirable that a calibration source be capable of being interrupted when not in use for calibration.